1. Field of the Invention
The invention relates to a process for the preparation of chloroformic acid methyl ester by reacting phosgene with methanol.
2. Discussion of Prior Art
The preparation of chloroformic acid methyl ester by passing phosgene into methanol in the temperature range from 0.degree. to 10.degree. C. is known (Houben-Weyl, volume 8, 101 et seq., 1952).
German Offenlegungsschrift No. 2,251,206 describes the continuous preparation of chloroformic acid methyl ester, in which the alcohol and phosgene are fed, the alcohol preferably being fed by means of a spray nozzle, into a reaction vessel, which in momentary equilibrium contains at least 20% by weight of phosgene in the reaction mixture, in such a way that the time for homogeneously mixing the alcohol into the reaction mixture is less than 5 seconds, an amount of the reaction mixture corresponding to the amounts of alcohol and phosgene fed in is removed and is freed from phosgene and hydrogen chloride and the phosgene is recycled into the reaction vessel.
It is known from German Offenlegungsschrift No. 2,453,284 that in the preparation of chloroformic acid methyl ester, the time for homogeneously mixing in the alcohol is less than 1 second, whereupon in momentary equilibrium an excess of phosgene in the reaction mixture now only of at least 2% by weight, a temperature of up to 70.degree. C. and a residence time of up to 300 minutes can be maintained.
According to the process described in German Offenlegungsschrift No. 2,704,262, for the preparation of chloroformic acid methyl ester, the liquid methanol is dispersed rapidly in the circulating chloroformic acid methyl ester (see pages 7 and 8). The phosgene is absorbed from the circulating reaction mixture in countercurrent in an absorption tower which is packed with glass Raschig rings or another packing material which does not have a catalytic action (page 8, lines 13 to 16). It is also stated (page 2, lines 2 to 3) that the liquid phosgene is dispersed in the chloroformic acid methyl ester.